Sight-testing apparatus.



No. 742,329. PATE'NTEDO'GT. 2.7, 1903.,

' e. JOHNSTON-.1 SIGHTTESTING APPARATUS.

APPLICATION FILED 00119 1902.

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U ITED, STATES Patented October 27, 1903.

GEORGE JOHNSTON, OFDETROIT, MICHIGAN:

SIG HT-TESTING APPARATUS.

SPECIFICATION forming part of Letters Patent No. 742,329, datedOctober 27, 1903.

Application filed October 9, 1902.

T at whom it may concern:

Be it known that I, GEORGE JOHNSTON, a citizen of the United States, residing at Detroit, county of Wayne, State of Michigan, have invented a certain new and useful Improvement in Sight-Testing Apparatus, of which the following is a specification, refer; ence being had to the accompanying drawings, which form a part of this specification.

My invention has for its object what I term a sight-testing apparatus, an instrument for correcting all errors of refraction in testing the eyes and fitting glasses therefor.

My invention consists of the construction, combination, and arrangement of devices hereinafter described and claimed, and illustrated in the accompanying drawings, in

which-- tion. Fig. 3is a partial front elevation. Fig. 4

is a partial rear elevation. Fig. 5 is a View in a vertical section through portions of the de vice. Fig. 6 is a section on the line 6 6, Fig. 2. Fig. 7 is a side view of a birefringent prism. Fig. Sis a front view of the same. Fig. 9 is a section of double prisms having their apexes together, showing other forms of prisms.

The purpose of my invention is toprovide an instrument of this class of superior efficiency and utility.

I carry out my invention as follows: Any suitable support is indicated at a. As shown, the support consists of a standard which may be engaged upon a suitable table, (indicated at b.) In the top of said support is journaled a tube, (indicated at 0,) upon which is mounted a disk 01, upon one face of which as upon the rear face thereof, is. a suitable scale, (indicated at e, Fig. 4,) the instrument being provided with an index-finger f, which may be mounted upon a portion of the support. The tube 0 is revoluble within a stationary case g, secured to the support a, said tube being provided at its forward end withany suitable prismatic structure, (indicated at h.) The forward end of the case is constructed with an observation-orifice t at the inner end of an eyepieoej. Forward of the'prismatic Serial No. 126,424. (No model.)

structure h the case is cut away, as indicated at k, to admit the insertion of testing-lenses, (indicated at 1,) the rear'faco of the front end of the case adjacent to said opening being provided with a suitable scale, "(indicated at m.) The tube 0 is revoluble with the disk 01. The prismatic structure h is such that when an observer looks therethrough at a distant object, as a circle, (indicated at n in Fig. 1,) said object will appear double to the eye of the beholder, the two visible forms of the object, as two circles, being adjacent one to the other, and in the normal eye the peripheries of the circles should contact the one with the other as the tube 0 is rotated to cause the one circle to traverse about the periphery of the other circle. In the normal eye the two circles should contact at their peripheries around the entire circumference thereof. An abnormal condition of the eye will be indicated by the two circles separating or overlapping at difierent meridians, the abnormal positions of the circle being indicated by the scale 2, while also the position of the lenslmay be indicated upon the scale m. I do not limit myself to a particular prismatic structure to be employed.

Birefringent prisms are indicated in Figs. 7 and 8; but any suitable prismatic structure can be employed within the scope of my invention and the same may be engaged with the tube a in any suitable manner. By this construction it will be evident that the tube 0 may readily be turned about as may be desired.

I prefer to bifurcate the support, as shown, Q

to receive the disk d, the finger f being mount-.

ed upon the rear bifurcated portion of the support. The disk (1 ismounted upon the rear end of the tube 0 and to the rear of the stationary case g.

What I claim as my invention is. 1. The combination of a support, an elongated revoluble tube journaled in said support and provided with a prismatic structure 1 through the prismatic structure, the forward end of the case having a rigid connection with the body of the case and constructed with an opening to receive a testing-lens between the observation-orifice and the prismatic structure.

2. The combination of a support, an elongated revoluble tube journaled in said support and provided with a prismatic structure at its forward end, a stationary case about the forward end of the tube secured at its rear end to said support and having its forward end projectingbeyond the forward end of said tube and provided with an observationorifice through which an object maybe viewed through the prismatic structure, the forward end of said case rigidly connected with the body of the ease and constructed to receive a testing-lens between the observation-orifice and the prismatic structure, the face of the ease in front of the prismatic structure pro vided with a scale.

3. The combination of a support, an elongated revoluble tube journalcd in said support provided with a. prismatic structure at its forward end, a disk mounted upon said tube toward the rear end thereof and revoluble therewith, a stationary case about the front end of the tube secured to said support and projecting beyond the forward end of said tube provided with an observation-orifice in front of the prismatic structure, said case constructed to receive a testing-lens between the observation-orifice and the prismatic structure, said disk provided with a scale, and an index-finger carried adjacent to said scale.

4. The combination of a support, an elongated tube journaled in said support provided with a prismatic structure at the forward end thereof, a stationary case engaged with the support above the forward end of said tube and projecting beyond the forward end of the tube and provided at its forward end with an observation-orifice for viewing an object through the prismatic structure, said case constructed to receive a testing-lens in front of the prismatic structure and provided with a scale in front of the prismatic structure, a disk mounted upon the tube toward the rear end thereof to the rear of said case provided with a scale and revoluble with said tube, and an index-finger mounted upon the support adjacent to said disk.

5. The combination of a support, an elongated revoluble tube provided with a prismatic structure at its forward end journaled in said support, a stationary case about the forward end of the tube secured to said support and projecting beyond the forward end of said tube, said case provided with an opening in front of the prismatic structure and with an observation-orifice in the end of the case in a line central to the prismatic structure, a disk mounted upon said tube toward the rear end thereof and to the rear of said case, said support bifurcated to receive said disk, the rear portion of the supportprovided With an index-finger.

In testimony whereof I have signed this specification in the presence of two subscribing witnesses.

GEO. JOHNSTON.

Vitnesses:

N. S. WRIGHT, M. M. STRUBLE. 

